This invention relates generally to pneumatic feeding devices and more particularly, it relates to a pneumatic feeding device for charging a container-type balance with a loose material supplied from a storing container via a rigid or fixed feeding conduit.
In conventional feeding devices of this type, known for example, from German Pat. No. 2 034 983, German Published patent application 2 733 201 or German Pat. No. 1 556 104, the feeding conduit is connected to the container of the balance via an elastic hose which adjusts itself to the movement of the balance beam. This known solution however is disadvantageous for several reasons. Because of the overpressure or the vacuum in the container of the balance the wall thickness of the employed hose has to be relatively large. As a consequence, the elasticity of such a massive hose connection has an influence upon the counter balance or the feeding of charges of the loose material in the container of the balance. In addition, such heavy duty hoses when operated under vacuum, exhibit a different elastic behaviour than when operated under pressure free conditions. For this reason, the calibration of the balance, if possible at all, can be made only with great difficulties. Furthermore, in spite of the elastic connection it is impossible to avoid horizontal pulling forces and the resulting rotary moment acting on the container of the balance during the charging operation.
As far as the known feeding devices are applied for dosing several components of the loose material, the individual feeding lines are united upstream of the elastic hose connection to the container of the balance. Upon charging the container to the desired weight the feeding is usually interrupted and consequently a residual amount of the loose material remains in the elastic hose. This residual amount is subsequently discharged into the container of the balance by a so called free blowing process. Apart from time losses the known dosing methods impair the accuracy of the weighting process inasmuch as residual loose material is different from case to case. The subtraction of this follow-up weight from the total weight of all components is therefore only an unsatisfying solution.